This dissertation consists of three essays in health economics, each of which utilize empirical methods combined with large administrative or survey datasets to answer policy-relevant questions. Chapter 1 examines the impact of increasing the minimum legal purchase age for tobacco products on youth smoking and other substance use using data from a large survey combined with difference-in-difference methods. I find that smoking decreases significantly following the increased minimum age for 18- to 20-year-olds. I also find evidence of positive spillovers to younger individuals (14- to 17-year-olds). I find no evidence to suggest substitution to other unhealthy substances is occurring. Chapter 2 examines the impact of financial transfers from the pharmaceutical industry to cancer drug prescribing physicians. Using an event-study approach, we find that these prevalent payments increase prescribing of related drugs by approximately 4.5%. We also present evidence that this increase is being driven by newer and more expensive drugs. We do not observe improvements in physician-level patient mortality. Chapter 3 studies the sugar-sweetened beverage (SSB) tax adopted by Mauritius in 2013 on youth SSB consumption and body-mass index (BMI). Using a difference-in-difference design, we find no impact on consumption or BMI; however, when we look at boys separately, we find that they are 11% less likely to report any SSB consumption.